Magento – Adding rel=”next”/”prev” tags based upon pagination

collection;headermeta-tagsseo

For SEO purposes, I'm attempting to add link tags to the head block so that I can reference the previous and next blog pages like so:

<link rel="prev" href="http://citygear.dev/blog?p=4">
<link rel="next" href="hhttp://citygear.dev/blog?p=6">

FWIW, I'm using the AW_Blog extension, though that's not of great consequence here.

Question

How can I retrieve the paginated collection as it is loaded in the content block so that I can add these tags to the header?

The snippet of my layout XML:

    <reference name="head">
        <block type="core/template" name="canonical_blog" template="page/html/canonical_pager.phtml" />
    </reference>
    <reference name="content">
        <block type="blog/blog" name="blog" template="aw_blog/blog.phtml">
            <block type="blog/product_toolbar" name="aw_blog_list_toolbar" template="catalog/product/list/toolbar.phtml">
                <block type="page/html_pager" name="product_list_toolbar_pager"/>
            </block>
        </block>
    </reference>

What I've tried

Per the layout file above, I've tried to add a template to the head so that I can render the link tags. I've tried within that file to reference the product_list_toolbar_pager block (as shown below), but the collection isn't available when loaded in the header.

$pager_block = $this->getLayout()->getBlock('product_list_toolbar_pager');

$pager_block->getCollection()->getSize() returns a fatal error because $pager_block->getCollection() is null

EDIT

Per Amasty's answer below, I tried the following, but $this->pagerBlock->getCollection() is still null.

Add a new Block (AW_Blog_Block_Relpager) with the following constructor:

protected function _construct()
{
    /**
     * @var Mage_Core_Model_Layout
     */
    $layout = Mage::app()->getLayout();

    /**
     * @var Mage_Page_Block_Html_Head
     */
    $headBlock = $layout->getBlock('head');

    /**
     * @var Mage_Page_Block_Html_Pager|null
     */
    $pagerBlock = $layout->getBlock('product_list_toolbar_pager');
    $this->pagerBlock = $pagerBlock;

    $this->setTemplate('aw_blog/blog_rel.phtml');

    /**
     * Append block to header block
     */
    $headBlock->setChild('rel_paginator', $this);

    parent::_construct();
}

Referring to the layout above, I added the following immediately underneath product_list_toolbar_pager

                <block type="blog/relpager" name="rel_paginator" />

Best Answer

Add a new block after the items inside the content block.

Inside this block access the header and toolbar blocks as

$this->getLayout()->getBlock('name');

Related Solutions

Magento – Magento SEO implement rel=”prev” and rel=”next” meta tags

I've found a workaround for magento2 to accomplish this, which I've published here, but for the sake of it being here should the gist go somewhere, I'll include the code below.

Basically, we just create a block that we include for catalog_category_view that checks the current selected category, and tries its best to figure out the paging.

There were some strange bugs in using the pager itself to generate the urls in which for some reason it wouldn't go past a certain page number if we had the limiting somewhat low (eg: 8 per page), and thus, workarounds were made.

If anyone has any suggestions or ways to improve this, i'd love to hear about it, but this works for now.

<?php

namespace Revival\Seo\Block;

use Magento\Framework\View\Element\Template;

/**
 * To make this appear in the header for the catalog, you'd need to add this as a block in ${THEME_DIR}/Magento_Catalog/layout/catalog_category_view.xml
 *
 * EG:
 *
 * <?xml version="1.0"?>
 * <page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="2columns-left" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
 *  <body>
 *      <referenceBlock name="head.additional">
 *          <block class="Revival\Seo\Block\HeaderPagination" name="pagination" template="pagination.phtml">
 *          </block>
 *      </referenceBlock>
 *  </body>
 * </page>
 *
 * All that the phtml really does is call $this->getPageHeaders(), omitted for brevity.
 *
 */

class HeaderPagination extends \Magento\Framework\View\Element\Template {

    /** @var $registry \Magento\Framework\Registry */
    public $registry = null;
    /** @var  $catalog \Magento\Catalog\Model\Category */
    public $category = null;
    /** @var  $logger \Psr\Log\LoggerInterface */
    public $logger = null;
    /** @var $context \Magento\Framework\View\Element\Template\Context */
    public $context = null;
    /** @var $toolbar \Magento\Catalog\Block\Product\ProductList\Toolbar; */
    public $toolbar = null;
    /** @var $pager \Magento\Theme\Block\Html\Pager */
    public $pager = null;
    public function __construct(Template\Context $context, array $data = [],\Magento\Framework\Registry $registry, \Magento\Catalog\Block\Product\ProductList\Toolbar $toolbar, \Magento\Theme\Block\Html\Pager $pager)
    {
        parent::__construct($context, $data);
        if($registry == null){
            $this->_logger->debug("[!] Received null registry from DI!");
        }
        $this->context = $context;
        $this->registry = $registry;
        $this->category = $registry->registry('current_category');
        $this->toolbar = $toolbar;
        $this->pager = $pager;
    }


    public function getPageHeaders(){
        //set pager and toolbar to use same collection, make sure they're both in agreement as to page limiting
        $this->toolbar->setCollection($this->category->getProductCollection());
        $tool = $this->pager->setCollection($this->category->getProductCollection());
        $tool->setShowPerPage($this->toolbar->getLimit());
        $has_prev_page = $has_next_page = false;
        $next_page_url = $prev_page_url = '';

        //calculate last page, round down to nearest int, 4.9 pages still means only 4 pages.
        $last_page =  intval((($this->category->getProductCollection()->count() - 1) / $this->toolbar->getLimit()) + 1);
        $current_page = $this->toolbar->getCurrentPage();

        //don't show a previous page on the first page, or if the last page is 1.
        if($current_page != 1 && $this->toolbar->getLastPageNum() != 1){
            $has_prev_page = true;
            $params = $this->getRequest()->getParams();
            //remove ?id param for category identification.
            $params['id'] = null;
            $params[$tool->getPageVarName()] = $current_page-1;
            $prev_page_url = $this->toolbar->getPagerUrl($params);
            //$prev_page_url = $tool->getPreviousPageUrl();
        }
        //if our page isn't the last page, show the next one.
        if($current_page != $last_page){
            $has_next_page = true;
            $params = $this->getRequest()->getParams();
            //remove ?id param for category identification.
            $params['id'] = null;
            $params[$tool->getPageVarName()] = $current_page+1;
            $next_page_url = $this->toolbar->getPagerUrl($params);
            //$next_page_url = $tool->getNextPageUrl();
        }
        if($has_prev_page){
            echo "<link rel='prev' href='{$prev_page_url}'>". PHP_EOL;
        }
        if($has_next_page){
            echo "<link rel='next' href='{$next_page_url}'>". PHP_EOL;
        }
    }
}